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Unraveling the Mechanism and Regioselectivity of the B12-Dependent Reductive Dehalogenase PceA
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Number of Authors: 3
2016 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 22, no 35, 12391-12399 p.Article in journal (Refereed) Published
Abstract [en]

PceA is a cobalamin-dependent reductive dehalogenase that catalyzes the dechlorination of perchloroethylene to trichloroethylene and then to cis-dichloroethylene as the sole final product. The reaction mechanism and the regioselectivity of this enzyme are investigated by using density functional calculations. Four different substrates, namely, perchloroethylene, trichloroethylene, cis-dichloroethylene, and chlorotheylene, have been considered and were found to follow the same reaction mechanism pattern. The reaction starts with the reduction of Co-II to Co-I through a proton-coupled electron transfer process, with the proton delivered to a Tyr246 anion. This is followed by concerted C-Cl bond heterolytic cleavage and proton transfer from Tyr246 to the substrate carbon atom, generating a Co-III-Cl intermediate. Subsequently, a one-electron transfer leads to the formation of the Co-II-Cl product, from which the chloride and the dehalogenated product can be released from the active site. The substrate reactivity follows the trend perchloroethylene>trichloroethylene >> cis-dichloroethylene >> chlorotheylene. The barriers for the latter two substrates are significantly higher compared with those for perchloroethylene and trichloroethylene, implying that PceA does not catalyze their degradation. In addition, the formation of cis-dichloroethylene has a lower barrier by 3.8kcalmol(-1) than the formation of trans-dichloroethylene and 1,1-dichloroethylene, reproducing the regioselectivity. These results agree quite well with the experimental findings, which show cis-dichloroethylene as the sole product in the PceA-catalyzed dechlorination of perchloethylene and trichloroethylene.

Place, publisher, year, edition, pages
2016. Vol. 22, no 35, 12391-12399 p.
Keyword [en]
cobalamin, density functional calculations, reaction mechanisms, reductive dechlorination, regioselectivity
National Category
Chemical Sciences
URN: urn:nbn:se:su:diva-135106DOI: 10.1002/chem.201601575ISI: 000382876500024PubMedID: 27459105OAI: diva2:1048199
Available from: 2016-11-21 Created: 2016-10-31 Last updated: 2016-11-21Bibliographically approved

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Siegbahn, Per E. M.
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